all ifs chevy trucks require 4 inches minimum with trimming to fit 35s 6 with no trimming on 35s and you can squeeze 37s in with some substantial trimming on a 6 inch lift and most need either the torsion bars tightened up or keys installed to fit 33s, but be careful you dont just turn them up too far cause you will hyper extend your shocks and kill them really fast, trust me i did it, the key kits come with a shock spacer to eliminate that problem

mine is stock with 33's and all i did was trim of a tiny piece of the corner of the bumper and it only rubbed there when i turned allt he way, you can even notice i trimmed. i just got a 3 inch body lift and i have a set of 35's that i want to put on it but i dont want to have to trim my fenders or anything so hopefully they willf it and not rub that hard if they do at all. and if they do then i guess i will just get a 2 inch torsion key lift